Fabric softeners, as finishing agents to provide softness to fabrics after laundry, usually provide antistatic effects as well as softness with regard to fabrics.
Previously, dimethyl dialkyl ammonium chloride (DDAC) was widely used as a fabric softener but after that, through quaternary ammonium salts of amino amine, imidazoline, imidazoline ester-type fabric softeners, there are currently being used most throughout the world cationic surfactant-containing fabric softeners which are prepared in the form of an esterquat by quaternizing ester compounds induced from fatty acids and tertiary amines.
However, since the fatty acids to be used in preparing the above fabric softeners are expensive, there have been lately developed methods of preparing fabric softeners from vegetable oils that replace expensive fatty acids in order to reduce manufacturing costs.
As methods of preparing fabric softeners by using oils, U.S. Pat. No. 5,869,716 discloses a method of preparing a fabric softener by reacting oil and hydroxyfunctionalized tertiary amine in the presence of a catalyst such as an alkali metal borohydride or an alkaline earth metal borohydride and then, reacting the obtained product with a quaternizing agent. U.S. Pat. No. 6,906,025 and U.S. Pat. No. 7,001,879 disclose a method of preparing a fabric softener by the transesterification reaction of oils in the form of triglyceride and amines in the presence of sodium borohydride, or sodium borohydride and calcium hydroxide. However, the methods of preparing cationic fabric softeners directly from oils as in those methods had high oil content in the form of unconverted glycerides, or resulted in fabric softeners having poor colors.
For this, there have been suggested methods for lowering the content of unconverted triglyceride and improving color by using strong alkali and borohydride catalysts, but these methods still result in high unreacted triglyceride content, and bad colors and odors.
Further, Korean Patent No. 854099 and No. 861699 each discloses a method of preparing an esterquat by performing the transesterification reaction of oils and tertiary amines at a high temperature under nitrogen atmosphere in the presence of alkali catalysts or titanium alkoxide catalysts, and then quaternizing the resultant product. However, the above method has a high reaction temperature and long reaction time due to a low solubility against reactants. Furthermore, since stearic acid is added to the oils in the transesterification reaction at a high temperature under nitrogen atmosphere, or a partially hydrogenated oil form is used by performing hydrogenation with regard to the oils prior to the transesterification reaction, it still has drawbacks that color enhancement effects are low and the content of oils in the form of glycerin and unconverted glycerides is high. As a result, for the color improvement of the fabric softeners, the use of a decolorant which causes skin trouble and irritation is essential after the reaction with quaternizing agents.